Note: Descriptions are shown in the official language in which they were submitted.
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WIRELESS ACCESS SYSTEM
FIELD OF THE INVENTION
The present invention is directed to digital loop carrier (DLC) systems and
in particular to telephone systems where DLC systems are combined with
wireless systems, and apparatus for facilitating this combination.
BACKGROUND OF THE INVENTION
Remote access systems are of increasing importance in providing cost
effective and efficient telephone services. Specifically, prior to the
development
of remote access systems, the end user or subscriber of the telephone services
could not be more than 3.5 miles (18,000 feet) from the service provider's
central office. This was due to the fact that the connections between the
central
office and the subscriber were direct, copper wire connections, and were
limited
to this distance due to attenuation. Moreover, these direct connections were,
and remain, costly to install and maintain.
One type of remote access system that has gained favor belongs to a
class of systems known as digital loop carrier (DLC) systems. These DLC
systems fall under the general category of carrier systems for subscriber
loops,
that consolidate traffic from hundreds of subscribers onto a small number of
physical lines to the central office, while extending the lengths for the
necessary
connections beyond the previous 3.5 mile (18,000 feet) limitation. DLC systems
are designed for placement within a carrier's local loop infrastructure and
serve
to provide telephone services, including data and video services, over trunks
using various media such as fiber optic and copper cables, between the central
office and the residential or business end user (subscriber), typically in
urban
and suburban locations.
Another type of remote access system that has been used for servicing
rural subscribers is a class of systems known as wireless local loop (WLL)
systems. In these systems, physical lines from central office are connected to
a
base unit, typically a radio-frequency transmitter/receiver for wireless
communication with remote station terminals (RST). These RSTs are
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connected, typically by wires, cables or the like, to the respective
subscribers.
One WLL system employed for this purpose is the StarAccessTM ERC wireless
communication system available from ADC/Teledata Communications Ltd. of
Herzlia, Israel.
Fig. 1 details a local exchange, employing a DLC system 1 and a WLL
system 2. In the DLC system 1, subscribers 10a, 10b, typically urban and
suburban subscribers, connect to a remote unit 12. This remote unit 12 is
typically a neighborhood site where the service is transitioned to lines 13a,
13b,
typically copper wires or coaxial cables, for delivery to the respective
subscribers 10a, 10b. This service transition is commonly referred to as a
local
loop. The remote unit 12 connects to a central unit (CU) 14 via trunks (trunk
lines) 16. The central unit 14 may be located within a central office 20 of
the
local exchange, where the actual switching is performed.
In the WLL system, subscribers, typically rural subscribers 10r,
communicate via their respective remote station terminal (RST) 22, with a base
unit 24, typically over radio frequencies (RF). The base unit 24 connects to a
central unit 25, analogous to central unit 14 for the DLC but adapted for the
WLL, in the central office 20 via trunks 16.
The DLC system 1 is exemplary of DLC systems in general, and as
shown in Fig. 2, typically comprises a central unit 14 and a remote unit 12.
The
central unit 14 connects to the central office 20 by lines 32, while
connections
with the remote unit 12 are made by trunks (trunk lines) 16, as detailed
above.
Other exemplary DLC systems are models DCS-20, DCS-30, DCS-40, all
commercially available from ADC/Teledata Communications Ltd., Herzlia, Israel
Turning also to Fig. 3A, there is detailed the remote unit 12 of the DLC
system 1, exemplary of remote units in general. The remote unit 12 includes
trunk cards 34 that connect to an allocation unit 36, that in turn connects to
line
cards 38. The trunk cards 34 interface the remote unit 12 with the trunk 16,
and
serve to extract relevant information for the remote unit, such as a
voice/data
telephone connection information that belongs to a subscriber of that
particular
remote unit 12. The allocation unit 36 allocates the bandwidth for each
subscriber of the particular remote unit. The line cards 38, detailed in Fig.
3B
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below, interface with the allocation unit 36 and transfer the voice/data
connection to the subscribers' individual lines, for example, lines 13a and
13b.
The line cards 38, shown in Fig. 3B, typically include physical interfaces
50, that communicate with subscriber lines, such as subscriber lines 13a, 13b,
in
communication with a routing unit 52. A DLC interface 54 is in communication
with the routing unit 52. The DLC interface 54 and routing unit 52 are
controlled
by a CPU 56.
Conventional systems, employing DLC systems and WLL systems
separately connected to the central office (exchange) in its infrastructure
exhibit
drawbacks. Specifically, with respect to DLC systems alone, these systems
require the running of wires/cables to each subscriber, and thus, the costs of
installation and maintenance of these lines remain high. Moreover, these costs
are particularly high in remote or sparsely populated areas, thus limiting the
numbers of subscribers that DLC systems can accommodate.
Additionally, by employing separate DLC and WLL systems, the service
provider must install and maintain components for two completely separate
systems, including separate trunk lines and hardware, one for the DLC system
and one for the WLL system. This results in increased costs. Moreover,
conventional DLC systems provide services, such as Synchronous Digital
Hierarchy (SDH) and Asymmetric Digital Subscriber Line (ADSL), that are not
available on conventional WLL systems, and as such, WLL subscribers can not
receive all of the services that subscribers on the DLC system are able to
receive.
SUMMARY OF THE INVENTION
The present invention improves on the conventional art, by combining
DLC systems with WLL systems, as integrated into local loops, to improve
voice/data transmissions. As a result, a service provider need only install
and
maintain a single system, the DLC system, as the WLL system connects to it, so
that the WLL system is supported by the DLC system. Thus the costs of
installation and maintenance of a system for servicing urban, suburban and
rural
subscribers is reduced substantially, as only a single line system, for the
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combined system, from the central office to the DLC system, is required, thus
eliminating the need for separate line systems for each of the DLC and WLL
systems. Additionally, as the WLL system is connected to the DLC system, the
WLL system subscribers can receive all of the services available to
subscribers
of the DLC system, such as connection to SDH rings and connection to ADSL
lines, and thus, eliminating any additional investment in the WLL system to
facilitate these additional services. Moreover, the system will have increased
range as its WLL system (components thereof) can be placed farther from the
central office, than with the presently employed WLL systems, that are
directly
connected to the central office (exchange).
Embodiments of the present invention are directed an access system and
to a line card apparatus, typically in a remote unit of a DLC system, and
methods for their use. These embodiments are such that voice/data
transmission services can be supplied to subscribers residing on conventional
wired lines, as well as wireless tines.
There is disclosed an access system comprising at least one digital loop
carrier (DLC) system and at least one wireless local loop (WLL) system with a
coupler for placing the at least one DLC system into operative communication
with the WLL system.
There is also disclosed a remote unit for a digital loop carrier (DLC)
system comprising at least one first card for supporting wired connections to
at
least one subscriber and at least one second card for supporting wireless
connections to at least one other subscriber. The at least one second card is
configured for operatively coupling the DLC system with a wireless local loop
(WLL) system, along which the at least one other subscriber is located.
Additionally, there is disclosed a line card for supporting a Wireless Local
Loop (WLL) system on a Digital Loop Carrier (DLC) system comprising a central
processing unit (CPU), an interface unit for buffering transmissions to and
from
the line card, this interface unit in operative communication with the CPU.
There
is at least one modem section in operative communication with the interface
unit, this at least one modem section configured for receiving digital data
and
converting this digital data into at least one digital signal, and for
receiving at
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least one digital signal and converting it to digital data. There is a base
band
section in operative communication with the at least one modem section, this
base band section including at least a digital to analog converter and an
analog
to digital converter. Also included are a signal combining (summing) section
in
operative communication with the at least one modem section and the digital to
analog converter, and a signal splitting section in operative communication
with
the at least one modem section and the at least one analog to digital
converter.
There is a intermediate frequency (IF) section in operative communication with
the base band section, this intermediate frequency section configured for
modulating the at least one analog signal onto a carrier signal and
demodulating
at least one signal from a carrier signal. The card is arranged such that the
CPU
controls operations of the at least one modem section, the base band section
and the intermediate frequency section.
It is preferred that there be a plurality of modem sections, preferably
twelve, with each modem section typically including a modem, a digital signal
processor (DSP) and at least one memory unit operably coupled thereto, with
the modem in operative communication with the digital signal processor.
There are also disclosed methods for transmitting voice/data to a WLL
system subscriber over a DLC system and from this WLL system subscriber to
the DLC system and thereover. This method includes providing a digital loop
carrier (DLC) system, providing a wireless local loop (WLL) system, coupling
the
DLC and WLL systems, and converting digital data from the DLC system into at
least one analog signal adapted for transmission over said WLL system. When
voice/data is transmitted from the WLL subscriber to the DLC system and
thereover (the reverse of the aforementioned transmission), at least one
carrier
signal from the WLL system, that includes the subscriber transmission, is
converted into digital data for transmission over the DLC system.
BRIEF DESCRIPTION OF THE DRAWINGS
Attention is now directed to the attached drawings, wherein like reference
numeral or characters indicate corresponding or like components. In the
drawings:
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Fig. 1 is a diagram of a conventional telephony system that utilizes
separate DLC and WLL systems;
Fig. 2 is a diagram of a conventional DLC system in a conventional
telephony system;
Fig. 3A is a diagram of a remote unit of the conventional telephony
system of Fig. 2;
Fig. 3B is a diagram of a line card used with the remote unit of Fig. 3A;
Fig. 4 is a diagram of a telephony system of an embodiment of the
present invention;
Fig, 5A is a diagram of a remote unit of one embodiment of the present
invention;
Fig. 5B is diagram of a portion of the remote unit of Fig. 5A;
Fig. 6 is a line card of one embodiment of the present invention; and
Fig. 7 is a diagram of a telephony system of an alternate embodiment of
the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Fig. 4, details the system 100 of the present invention where a DLC
system connects to a WLL system (forming a portion of the system 100), via a
remote unit 102, in accordance with the present invention. Subscribers 103a
(here urban but could also be suburban), receive service over the DLC system,
as they are directly connected thereto by physical lines 104, while other
subscribers 103b-103d, in urban 103b, suburban 103c and rural 103d, locations,
receive service by wireless communications (arrows 105) over the WLL portion
of the system 100. In this system 100, connections are such that all of the
components are arranged to define both transmitting (Tx) and receiving (Rx)
paths for data.
The DLC system is formed by the central unit (CU) 14, internal or external
to the central office 20 or exchange (connected by lines if the central unit
14 is
external to the central office 20), that in turn, connects to the remote unit
102 via
trunks) 109. The trunks) 109 could be wired or wireless, and if wireless could
be a satellite system or the like.
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The WLL portion of the system 100 is formed of at least one base unit
110, for example, a base radio frequency (BRF) unit, and remote station
terminals (RSTs) 112. The RSTs 112 connect to the respective subscribers
103b-103d by conventional lines. The WLL portion of the system 100 connects
to the DLC system at the remote unit 102 via a line card 126 (the remote unit
102 and line card 126 are shown in detail in Figs. 5A, 5B and 6 and described
below). The base unit 110 is preferably a radio frequency (RF) unit, that
transmits and receives signals, preferably RF signals, although other
transceiving units are also permissible. The base unit 110, is in
communication
with the remote unit 102 via conventional line connections (detailed below).
In one embodiment of the WLL portion, the components for the wireless
transmitting and receiving, including the RSTs, are provided by components
from the StarAccessTM ERC system, commercially available from ADC/Teledata
Communications Ltd. of Herzlia, Israel. In other embodiments, CDMA, TDMA,
analog CMA or other wireless technology are used.
The system 100 forms a transmitting (Tx) path as the data is received at
the central office 20 and is sent to the central unit 14. The central office
20
includes a switch in communication with the central unit 14, that multiplexes
the
transmission (signal) on the trunks) 109, preferably a digital line(s), to the
remote unit 102. This digital data is then modulated on analog signals for
transmission to the base RF units 110 and to directly connected subscribers
103a. From the base RF unit(s) 110, RF transmissions are received by the
respective RSTs 112 (these RSTs configured with hardware and software for
accommodating RF transmissions) and passed to the corresponding subscribers
103b-103d.
In a receiving (Rx) path for the system 100, directly connected
subscribers 103a, transmit their calls (voice/data) to the remote unit 102
over
physical lines 104. Subscribers 103b-103d along the WLL portion employ the
RF transmitter or the like, for sending their calls to the base RF unit 110,
with the
call then sent to the remote unit 102. In the remote unit 102, the modulated
analog signal is converted into a digital signal and sent over trunks) 109 to
the
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central unit 14 and past the switch in the central office 20 and outward in
accordance with conventional telephony.
Fig. 5A shows the internal logical connectivity between components in the
remote unit 102 of the present invention. The remote unit 102 includes trunk
cards 120 (for example, Part No. 712-y1803B from ADC/Teledata
Communications Ltd., Herzlia, Israel), that connect to an allocation unit 122,
that
in turn connects to line cards 124a, 124b and a WLL line card 126, the WLL
line
card 126 in accordance with an embodiment of the present invention. Line
cards 124a, 124b are adapted for physical wired links, and for example, can be
Part No. 712-419100 from ADC/Teledata Communications Ltd., Herzlia, Israel,
while the WLL line card 126 is adapted for wireless links. While two trunk
cards
120, two "wired" line cards 124a, 124b and one WLL or "wireless" line card 126
are shown, this is exemplary only as any number of these trunk and line cards
can be used, provided there is at least one "wireless" line card, in
accordance
with the desired embodiment of the present invention.
In Fig. 5B, there are detailed physical connections in the remote unit 102
that form the DLC bus 127 of allocation unit 122 and line cards 124a, 124b and
126 (as shown enclosed by the broken lines in Fig. 5A, for illustration
purposes
only). Data from and to the allocation unit 122 travels to and from the line
cards
124a, 124b, 126 over a series of Point-To-Point connections (PTPs) 128a, 128b
and buses 129a, 129b.
Each PTP 128a, 128b is a special path between the allocation unit 122
and each line card. Each PTP 128a, 128b has N or greater than N connections
with the allocation unit 122, N corresponding to the total number of line
cards in
the remote unit 102. Each specific connection of the N connections then
extends from the respective PTP 128a, 128b, to the respective line card. While
line cards shown here are line cards 124a, 124b, 126, this is exemplary only,
as
the system is suited for N number of "wired" 124a, 124b and "wireless" 126
line
cards. Typically, one PTP, such as PTP 128a is CELL oriented while the other
PTP 128b would be TDM oriented. Moreover, in a system typical to that shown
in this embodiment, PTP 128a may be approximately 155M, while PTP 128b
may be approximately 8MBPs on each PTP Branch.
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The busses 129a, 129b typically employ single connections to the
allocation unit 122 and N line cards, here, for example, line cards 124a,
124b,
126. Typically, one bus 129a is SDH oriented and can, for example, be
approximately 155-622M, while the other bus 129b would be TDM oriented, and
can, for example, be approximately 266M.
In this remote unit 102, connections are such that the components are
arranged to define both transmitting (Tx) and receiving (Rx) paths for data.
In
the transmitting path, digital data, typically a digital signal, from the
respective
trunk 109 (Fig. 4) is received by a corresponding trunk card 120, and passed
to
the allocation unit 122, where the data signal is directed and routed to the
proper
line card 124a, 124b, 126 over the internal DLC bus 127. Should the data be
directed to a conventionally connected subscribers, such as the DLC system
subscribers 103a (Fig. 4), the digital data is sent to, for example, line
cards
124a, 124b. Should the data be allocated to a WLL subscriber 103b-103d (Fig.
4), WLL line card 126 is employed. Here, the digital signal/data is converted
to
an analog signal/data for transmission to the base RF unit 110 (Fig. 4), this
base
RF unit 110 including a converter for converting the received signal into an
RF
signal(s), for transmission to the WLL subscribers 103b-103d as detailed
above.
In the receiving path (Rx), analog signals from the subscribers 103a and
base RF (BRF) unit 110 enter the line cards 124a, 124b, 126, where they are
converted to digital data. This digital data is then passed through the
allocation
unit 122, where it is directed, and then through the respective trunk cards
120, to
the respective trunks 109, for transmission to the central unit 14 (Fig. 4).
Fig. 6 details the WLL ("wireless") line card 126 of an embodiment of the
present invention. Although only a single WLL line card is shown, this is
exemplary only, as multiple WLL line cards may be used with the present
invention. The components of the WLL line card are arranged so as to provide
both transmitting (Tx) and receiving (Rx) paths.
Card 126 is capable of handling several subscribers, with some
subscribers able to be served simultaneously, whereby each card preferably
includes multiple modems. The combined information of all subscribers in the
card 126 is transmitted, preferably via radio frequency, to the subscribers.
The
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card 126 serves to transform DLC traffic into a radio frequency (RF) data
stream
that is sent from the base unit 110. The line card 126 includes a CPU 132 in
communication with a DLC Interface 134, single or plural, modem sections)
136, of which there are preferably twelve, logic sections 138 (Tx section),
139
(Rx section), employing technologies such as FPGA or ASIC, a base band
section (BB) 140, and an Intermediate Frequency (IF) section 142.
The DLC interface 134 connects to the DLC bus 127 and serves as a
buffer between the DLC bus 127 and the modem sections) 136. The CPU 132
interacts with DLC interface 134 by providing it with allocation information,
for
example, information as to destination, source, rate, signaling, etc., for the
entering data/transmission. Moreover, the DLC interface 134 signals one of the
preferred twelve modem sections 136, that a transmission is entering.
Each modem section 136 preferably modulates the information of each
radio channel on a carrier frequency and vice versa. Each radio channel can be
for single or multiple subscribers. Each modem section 136 includes a modem
150, in communication with a digital signal processor (DSP) 152, preferably
coupled with a memory unit 154. The DSP 152 processes data associated with
data received over the DLC bus 127, controlled by commands received from the
CPU 132, and creates a digital representation of an analog signal, that comes
from the DLC bus 127, preferably with error correction signals. This digital
representation of an analog signal is a digital signal formed of analog
samples of
digital signals) coming from the DLC bus 127, filtered and corrected for phase
errors (this filtering and correcting performed in the respective modem
section
136).
This digital signal is sent to the modem 150. Each modem section 136 is
available as a single unit and for example can be Teledata Part No. 712-
71101 D, from ADC/Teledata Communications Ltd., Herzlia, Israel.
The Tx section 138 processes the digital signals) by algorithms, such as
Fast Fourier Transforms (FFT) with filtering or weighting, in order to combine
(sum) the digital signals as received from each modem section 136 and produce
a combined (summed) digital signal. This Tx section 138 is adapted for
functioning along the transmitting (Tx) path for the WLL line card 126. This
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section is available as Teledata Part No. 752-71200B, from ADC/Teledata
Communications Ltd. Herzlia Israel.
The Rx section 139 is adapted for functioning along the receiving path for
the WLL line card. This Rx section 139 employs Inverse Fast Fourier
Transforms (IFFT) with filtering or weighting, in order to analyze the signal
from
the base band section 140 and split the signal to each modem 150 (of the
preferred 12 modems). This Rx section is available as Teledata Part No. 752-
710000, from ADC/Teledata Communications Ltd., Herzlia, Israel.
The base band section (BB) 140, includes signal converters. This section
includes a digital to analog converter and filter 156, in communication with
the
Tx section 138, and an analog to digital converter and filter 157 in
communication with the Rx section 139, for converting the signals received in
this section 140 accordingly.
The IF section 142 includes a modulator as well as a demodulator. When
in the transmitting (Tx) path, the modulator functions such that the analog
signal,
as received from the base band unit 140 is modulated on a carrier signal and
sent to a base unit 106, typically by coaxial cable or other conventional
carrier.
When in the receiving (Rx) path, the demodulator functions to extract the
analog
signal from the coaxial cable or other conventional carrier and send it to the
base band section 140.
In the transmitting (Tx) path, the DLC interface 134 receives the
transmission, typically a digital signal(s), from the DLC bus 127. The
signals) is
then taken according to the allocation information from the CPU 132 and
coupled to the respective modem 150 (in the respective modem section 136). In
the respective modem section 136, the signal moves from the modem 150 to a
DSP 152, where it is processed, in accordance with the allocation information
provided from the CPU 132. This digital signal is then passed through the
respective modem 150 to the Tx section 138, where it is processed by
algorithms such that it is combined (summed) with other similar digital
signals as
received from the other modem sections (as processed in a manner identical to
that described above).
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The signal is now sent to the base band section 140, where it is
converted to an analog signal by being passed through the digital to analog
converter and filter 156 of this section 140. The analog signal is sent to the
IF
section 142, where it is modulated onto a carrier signal and sent to the base
unit
110, typically by coaxial cable of other conventional carrier.
In the receiving (Rx) path, the analog signal is demodulated from the
signal received from the base unit 110, in the IF section 142. The analog
signal
is then sent to the base band section 140, where it is converted into a
digital
signal upon its being passed through an analog to digital converter and filter
157
in the base band section 140. The digital signal is sent to the Rx section
139,
where it is analyzed (split) to extract modem signals, preferably twelve modem
signals corresponding to the preferred twelve modems, with each extracted
signal sent to the respective selected modem section 136. In each modem
section 136, the digital signal is converted to DLC bus digital data. The
modem
150 then sends this data to the DLC interface 134, where it enters the DLC bus
127, for transmission to the central office 20 (Fig. 4).
Turning now to Fig. 7, there is a second system 200 in accordance with
the present invention. This system includes a modified DLC with wireless local
loop capabilities. This system enables the service provider to enlarge
coverage
of the system to sites where conventional lines can not be deployed or would
be
cost prohibitive.
In this system 200, the central unit (CU) 14, in communication with the
central office 20 (exchange) (via lines 32), connects to a remote unit 202, in
accordance with the remote unit 102 above, in a manner where all exchange
traffic is multiplexed into a high speed physical trunk. Here, the trunk is a
synchronous digital hierarchy (SDH) protected ring 208.
The remote unit 202 extracts the relevant telephony information form the
SDH ring 208 and directs it to a local subscriber line 213, to a directly
connected
subscriber 213a, by a conventional line card, as detailed above, or over
conventional lines or the like. While only a single remote unit 202 is shown,
multiple remote units along the SDH ring 208 are also permissible. The remote
unit 202 also employs WLL line cards of the present invention (not shown in
this
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figure but shown as line card 126 above and described above), that connect via
lines 214 (as detailed above) to a base RF (BRF) Units 218a-218c, similar to
the
BRF unit 110 detailed above.
The base units 218a-218c communicate with the remote station terminals
(RSTs) 220a, 220b, 221 a, 221 b, 221 c (in accordance with those detailed
above), by wireless links (arrows 224) and form the WLL portion of the system
200. These RSTs 220a-220b and 221 a-221 c connect to subscribers, both voice
226 and data 228, by conventional connections, typically wired, as detailed
above. With respect to base RF units 218b and 218c, base unit 218c is
preferably an alternate RF unit for wireless transmissions to the remote
station
terminals 221 a-221 c.
The SDH ring 208 is controllable by a computer 240, and can be
interfaced with an ATM network 242 or the like. It is preferred that the
computer
240 and ATM network interface at the central unit 14.
While preferred embodiments of the present invention have been
described, so as to enable one of skill in the art to practice the present
invention,
the preceding description is intended to be exemplary only. It should not be
used to limit the scope of the invention, which should be determined by
reference to the following claims.
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